Slice the mushrooms and add them to a skillet with the cooking oil, garlic powder, crushed red pepper, and half of the salt and pepper. Sauté over medium until the mushrooms have released all of their water and it has evaporated out of the skillet. Set the mushrooms aside.

Thaw the frozen spinach then squeeze out as much of the water as possible. You should have about one cup of spinach (loosely packed) once squeezed.

Add the mushrooms, spinach, shredded mozzarella, sour cream, and another ⅛ tsp each of salt and pepper to a bowl, then stir to combine.

Add about ½ cup of the cheesy spinach mushroom mixture to each tortilla, spread it out to cover one side of the tortilla, then fold to close.

Cook the quesadillas in a skillet over medium heat until brown and crispy on the outside and melty on the inside.

Slice the quesadillas and serve!